According to the prior art capacitors are connected in series if the voltage to be applied is greater than the permissible voltage of an individual capacitor. Electrolytic capacitors (ELKO) are available in sizes up to approx. 500 V rated voltage for example. Therefore for applications which provide for the storage of electrical energy in electrolytic capacitors with voltages above 500 V, two or more electrolytic capacitors have to be connected in series.
It is known for example to use a number of input capacitors for inverters, which are used to feed electrical energy from alternative power sources into a power network. With solar generators in particular high voltages occur at the input of the inverter, for which reason a series circuit of a number of electrolytic capacitors is generally provided for input-side energy buffering.
To divide the input voltage present evenly between a number of capacitors, according to the prior art a voltage divider is arranged parallel to the capacitors. In the simplest instance the voltage divider consists of high-impedance resistances, with a resistance being connected parallel to each capacitor.
Such series circuits comprising a number of capacitors have the disadvantage that the desired voltage limiting for the individual capacitors fails when a fault occurs, during which a capacitor short circuits. The shorting of a capacitor necessarily results in the input voltage then being divided between the remaining unshorted capacitors.
This problem is resolved in the known manner by over-dimensioning the capacitor circuit. Therefore for example additional capacitors are arranged to compensate for the failure or shorting of individual capacitors. This has the disadvantage of increasing component costs and the need to provide an additional circuit indicating the failure of a capacitor.
Another known measure for protecting capacitors is the arrangement of fuses in the current path of each individual capacitor. In the event of a short circuit the blown fuse interrupts the current flow and the remaining capacitors are not charged further. Before resuming operation, the fuse must be changed and the cause of the short circuit must be eliminated.